Machine tools, preferably lathes

ABSTRACT

A machine tool for successively machining opposite ends of short-length workpieces has a hollow spindle. A chuck having a hollow inside is provided on at least one end of the hollow spindle. The hollow space of the spindle and chuck provides a smooth and continuous guide surface for easy and successive transfer of the workpieces therethrough.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to machine tools, and particularly lathes, forprimary and secondary machining, successively, a number of short-lengthworkpieces.

The term "short-length workpieces" as hereinused means a workpiece whichis holdable by a chuck. Thus, elongated bars, rods and the like areexcluded.

2. Description of the Prior Art

It is frequently necessary in the field of machining to execute aprimary and a secondary machining successively on opposite ends,respectively, of each of a large number of similar workpieces with asingle machine tool.

A representative conventional method for this uses two rotatablespindles carrying chuck units arranged in opposition to each other, atleast one of these spindle reciprocating along the common axis of thetwo. In this case, the primary machining is carried out while theworkpiece is held by one chuck unit, and then the secondary machining isexecuted upon transfer of the workpiece to the second chuck unit. Forthis, reference may be had to U.S. Pat. No. 4,457,193.

It is also known to use one spindle carrying a single chuck unit. Inthis case, the primary machining is carried out while the workpiece isheld by the single chuck unit, and then either a robot or a loaderprovided with a position reverser is used. The already primarymachinedworkpiece is released from the chuck unit, subjected to theposition-reversing operation of the robot or loader and rechucked in thesame chuck unit.

In the former case, with the two spindles, at least one of the spindlesmust be mounted on a reciprocable feeder, thereby requiring increasedspace and manufacturing cost for the machine tool.

In the latter case, the robot or loader must be additionally provided,again requiring increased space and cost.

SUMMARY OF THE INVENTION

It is, therefore, an object of the present invention to provide animproved machine tool capable of performing primary and secondarymachining and intermediate feed of a workpiece therebetween in a highlysmooth and economical manner with an amazingly simplified mechanism.

For this and further objects, the invention provides a machine tool, andparticularly a lathe, for machining successively a number ofshort-length workpieces in primary and secondary steps. It has a spindlestock and a hollow spindle rotatably mounted on the spindle stock. Afirst tool head is shiftable on the machine tool in proximity to one endof the hollow spindle for execution of the first, i.e. primary,machining step. A second tool head is shiftable on the machine tool inproximity to the other, i.e. opposite, end of the hollow spindle forexecution of the second, i.e. secondary, machining step. A chuck unit isprovided at the other end of said hollow spindle for holding successiveprimary-machined workpieces. The inside wall surface of the hollowspindle and inside surface of the chuck unit jointly provide a smoothand continuous guide surface for the workpieces.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and further objects, features and advantages of the inventionand the manner of attaining them will become more apparent and theinvention itself will be best understood by reference to the followingdetailed description of preferred embodiments of the invention taken inconjunction with the accompanying drawing, in which:

FIG. 1 is a schematic top plan view of a preferred embodiment of themachine tool of the invention;

FIG. 2 is a schematic longitudinal elevation, partly in section, ofessential portions of the machine tool shown in FIG. 1, including aspindle stock, a spindle and a chuck unit;

FIG. 3 is a schematic longitudinal elevation, partly in section, of afurther preferred embodiment of the essential portions shown in FIG. 2;

FIG. 4 is a schematic plan view, partly in section, of a portion of theembodiment of FIG. 1 during transfer operation on workpieces therein;

FIG. 5 is a schematic plan view of a portion of the embodiment of FIG. 1with a workpiece therefor;

FIG. 6 is a partly-sectional elevational view of a workpiece-feedportion of the embodiment of FIG. 1 with workpieces therefor;

FIG. 7 is an enlarged, partly-sectional elevational view of a pusher-rodportion of the portion shown in FIG. 6; and

FIG. 8 is a schematic top plan view of a still further preferredembodiment of the machine tool of the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

In FIG. 1, a hollow spindle 2 is rotatably mounted on a spindle stock 1.The spindle stock is stationarily mounted on a supporting surface of arigid base which is not shown only for convenience of the drawing. Thesupporting surface of the base may be horizontal, as may be easilysupposed from FIG. 1. However, if occasion may desire, the supportingsurface may be inclined at any desired angle in another embodiment (notshown). Thus, in an extreme case, the supporting surface may bevertical.

The hollow spindle 2 has a passage 2a therethrough, chucks C₁ and C₂being integral with the spindle at opposite ends of the passage. Spindle2 is mounted in a pair of ball bearings 6. The spindle is rotated by adrive wheel 3, which is fixedly mounted thereon. The drive wheel 3 isformed, as a preferred example, by a pulley, as shown in schematicsection in FIG. 2. An endless belt 5 is tensioned around the drive wheel3 and a further pulley 4, which is direct coupled with the spindle of amotor M₁. Thus, with energization of the motor M₁, the hollow spindle 2is caused to rotate.

In addition, it will be seen from FIGS. 1 and 2, that an inside,workpiece-gripping portion of each of the chucks and the inside hollowpassage 2a of the spindle have a common cross-sectional configuration,preferably circular, thereby providing a smooth and continuous insideguide surface. At the outside of each of the chucks C₁, C₂, there are aplurality of, and preferably three, chucking jaws 7, which are movableradially, as conventional. As the chuck operating mechanisms, anyconventional devices can be used, and thus, they are not shown.

In FIG. 3, the hollow spindle has two, slightly spaced, aligned spindlesections 2A, 2B. At each of the outer ends of the spindle sections,there is provided, as before, a chuck unit C₁, C₂, respectively. Thespindle sections are driven through pulley 3, endless belt 5 and furtherpulley 4 from respective drive motors M₁, so as to be driven at mutuallyindependent rotational speeds.

Returning to FIG. 1, tool heads T₁ and T₂ are provided on the machinetool at the respective chuck units C₁, C₂. The tool heads T₁, T₂ supportrespective turrets t₁, t₂, which are rotatable, as commonly known, atthe operator's will. The tool heads are mounted on respective toolslides S₁, S₂, so as to shift in perpendicular directions X and Z.

The tool slides S₁ and S₂ have similar structures and functions. Eachhas a slider 10, which is slidable along a guide 12a of a bed 12 in thedirection Z to feed a tool (not shown). This tool feed in the directionZ is effected by a feed screw 11, which is driven by a servo-motor M₂.Another slider 13 is supported on the slider 10 and slidable in thedirection X by a cross feed screw 14, which is driven by anotherservo-motor M₃. The tool head is supported on the slider 13.

According to one mode of operation of the machine-tool embodiments sofar described, machining a short-length workpiece W (shown in FIGS. 4and 5) may be carried out in the following way.

At first, the workpiece W is held in chuck unit C₂ on one end of thehollow spindle 2 by its chuck jaws 7 for a primary or first machiningoperation. For example, turning can be executed by a tool at 16 in FIGS.5 on the turret t₂.

Upon completion of the foregoing first machining operation, therotational drive of the spindle 2 (by motor(s) M₁, as described above)is stopped and the turret t₂ is rotated to the position of a pusher rod19 (FIG. 4). The turret t₂ is slid with the tool slide S₂, until thepusher rod 19 opposes the workpiece W as schematically illustrated inFIG. 4. Further, the chuck C₂ is loosened, and the tool slide S₂ thenadvances the pusher rod 19 into the hollow space 2a of the spindletowards other chuck C₁. By this operation, the semi-fabricated, i.e.primary-machine workpiece W could be pushed into the inside space of thechuck C₁. In practice, however, a number of such semi-fabricatedworkpieces are accumulated in the hollow space 2a of the spindle. Inthis way, successive recharges of workpieces into the other chuck C₁ canbe economically and efficiently executed one after another with ashorter working, i.e. workpiece-pushing stroke of the pusher rod.

Upon introduction of each semi-fabricated workpiece W into other chuckunit C₁, its jaws 7 are tightened for holding it. The position of thethus introduced workpiece is determined by a stopper 20 on the turrett₁. Upon completion of this chucking operation, the turret t₂ is rotatedto position a tool at the workpiece, the spindle 2 is drivingly rotatedand a secondary machining operation is executed with a tool on turrett₁. The secondary machining can be, for instance, an inside turningoperation with the tool 17 shown in FIG. 5, and is on the opposite endof the workpiece W from the primary machining operation.

While the secondary machining is being executed, a further workpiece canbe held in the chuck C₂, and thus, the primary and secondary machiningsteps can be performed simultaneously. Tightening and loosening of thetwo chucks C₁ and C₂ can be done in a parallel manner.

According to the invention, the inside surface 2a of spindle 2 and theinside hollow surfaces of chucks C₁, C₂ provide, jointly, a smooth,stepless and continuous guide surface, as shown in FIG. 4. As a result,positive and smooth successive conveyances of primary-machinedworkpieces along the guide surface is assured.

As clearly seen from the foregoing description and according to the mainfeatures of the invention, the primary-machined short-length workpiecesare transferred directly from the position of such machining to thechuck for execution the secondary machining through the hollow space ofthe spindle, thereby attaining quicker and more positive workpiecetransfer with a simpler, smaller structure.

It is also possible to arrange a number of the foregoing embodiments ina matrix of generally parallel manufacturing lines, thereby realizingsystematic and flexible control of a system for the introduction anddischarge of a large number of machining and machined workpieces havingconsiderable advantages and benefits.

FIGS. 6 and 7 show a mechanism for successive transfer of a plurality ofworkpieces W to the chuck C₂ for the primary machining. One end of apusher bar 22 is fixedly attached to the piston rod 24 of a pneumaticcylinder unit 23. The opposite end of the pusher bar 22 has a recess 25with a general configuration for receiving one of the workpieces W. Ahopper or chute 26 has a conventional structure for feeding successiveworkpieces W to a leading or lowest outlet end where one will be caughtin the recess 25 and pushed from the outlet and when the pneumaticpiston and cylinder unit advances bar 22 from a retracted position pastthe outlet end of the chute 26. With further such advancement of thepusher bar, the workpiece is introduced into the chuck C₂, and so on forsuccessive workpieces.

In FIG. 8, another embodiment of the invention is illustrated. In thisembodiment, two spindle stocks 1A and 1B are fixed in parallel.

A spindle 2 on the first spindle stock 1A is provided only at one endwith a chuck unit C₄. A hollow spindle 2 on the second spindle stock 1Bis also provided only at one, but opposite end with a chuck unit C₃. Thehollow spindle 2 of the second spindle stock 1B is open at its other,opposite end, which end is situated in the neighborhood of the chuckunit C₄.

A first tool head T₃ is provided at the end with chuck unit C₃, and asecond tool head T₄ is provided at the end with chuck unit C₄. The toolheads T₃ and T₄ are mounted on respective tool slides S₃ and S₄, whichare substantially similar to the aforementioned tool slides S₁ and S₂shown in FIG. 1. Thus, each of these tool slides S3 and S4 comprisesservo-motors M₂ and M₃, feed screws 11 and 14, and sliders 10 and 12.Further, the tool heads T₃ and T₄ have turrets t₃ and t₄, respectively.Turret t₃ is provided on its periphery with a work holder 27, and turrett₄ is provided on its periphery with a workpiece holder 28 as well as apusher rod 19a, which projects from its front surface.

In operation, at first, a short-length workpiece (not shown in FIG. 8)is held in chuck unit C₄ while its spindle 2 is rotated. Primarymachining is then executed on the workpieces in the chuck unit C₄ by amachining tool (not shown) on the turret t₄ of tool head T₄.

When the primary machining is finished, the rotation of the spindle 2with chuck unit C₄ is stopped, the chuck unit C₄ is loosened, and theprimary-machined workpiece is held by the work holder 28 of turret t₄,which removes the workpiece from the chuck unit C₄. Then, tool slide S₄is shifted to bring the workpiece to such a position relative to theopen end and inner hollow space 2a of the hollow spindle 2 of thespindle stock 1B as to be ready for advancing the workpiece into thehollow space of the spindle towards the chuck C₃. Then, the workpiece isso pushed by the pusher rod 19a of the turret t₄ by operation of thetool slide S₄ into the chuck C₃.

Upon conveyance of the primary-machined workpiece into the chuck C₃, thelatter is retightened for chucking the workpiece, the hollow spindle 2is again brought into rotation, and the workpiece is subjected tosecondary machining by use of the tool on turret t₃. After this, chuckC₃ is loosened and the workpiece is removed therefrom with a workpieceholder 27 on the turret t₃.

It will be seen from the foregoing description also that theprimary-machined, short-length workpiece is simply and rapidly conveyedfor secondary machining without broadening the conveying space. Indeed,the inside of the hollow spindle is used to prepare for thenext-succeeding secondary machining operation.

What we claim is:
 1. A machine tool for machining successively a numberof short-length workpieces, comprising, in combination:a first spindlestock; a first spindle rotatably mounted on said first spindle stock; afirst chuck unit mounted on one end of the first spindle, a secondspindle stock; a second spindle rotatably mounted on said second spindlestock and disposed close to, and in parallel relation to said firstspindle, said second spindle being a hollow spindle having one endthereof disposed adjacent to said first chuck unit; a second chuck unitmounted on the other end of the second spindle, the inside wall surfaceof the second chuck unit and that of said second spindle providingjointly a smooth and continuous guide surface; a first tool headprovided in the proximity of said first chuck and said one end of thesecond spindle; a first turret mounted on the first tool head andsupporting first machining tools, a first workpiece holder and pushermeans; first tool slide means for shifting the first tool head in afirst direction parallel to said spindles and in a second directionperpendicular thereto, thereby to cause said first machining tools tocarry out a primary machining operation on a workpiece held by saidfirst chuck, to cause said first workpiece holder to hold and transferthe workpiece which has been subjected to the primary machiningoperation and released by said first chuck to a position adjacent tosaid one end of the second spindle, and then to cause said pusher meansto push the workpiece into the hollow interior of the second spindle toconvey the workpiece into said second chuck unit along said continuousguide surface; a second tool head provided in the proximity of saidsecond chuck unit and the other end of the first spindle; a secondturret mounted on the second tool head and supporting second machiningtools and a second workpiece holder; and second tool slide means forshifting the second tool head in said first and second directions,thereby to cause said second machining tools to carry out a secondarymachining operation on the workpiece held by said second chuck unit andthen to cause said second workpiece holder to remove from the secondchuck unit the workpiece which has been subjected to the secondarymachining operation.
 2. The machine tool of claim 1 wherein said pushermeans supported on the first turret is a pusher rod extending in saidfirst direction towards the spindle stocks.